1. Field of the Invention
The present invention relates to a control method and device for stopping a reel on which a plurality of symbols including blank symbols are arranged in rotational direction.
2. Description of the Related Art
A slot machine has a plurality of, generally three, four or five, reels built in. Various symbols are arranged on a peripheral surface of the reel. In a stopped state of the reel, at least one of the symbols is adapted to be observed through a symbol display window relative to each reel. Upon starting a game, three reels are simultaneously rotated. When all of reels are stopped by a player's operation of a stop button or by an automatic stop mechanism, presence of winning and kind of winning are determined in accordance with a combination of symbols displayed in the symbol display window.
On the reel, character symbols and blank symbols are arranged at constant pitch. The character symbol has a letter pattern or a character pattern, for example, "7", "BAR" and "cherry". The blank symbol does not have any pattern. As shown in FIG. 4, such a reel is manufactured by sticking a symbol sheet 3 on an outer periphery of a reel main body 2 assembled in cylindrical frame form. The symbol sheet 3 is a strip-like sheet having the identical length L with peripheral length of the reel main body 2. Various symbols are printed on the symbol sheet 3 at constant pitch P. The symbol sheet 3 is stuck to the reel main body 2 such that top of the symbol sheet 3 is adjusted to a predetermined home position index S.
The reel main body 2 is directly connected to a drive shaft of a step motor 5. The step motor 5 is rotated according to the number of drive pulses supplied thereto. The number of drive pulses is counted by a counter 6. The reel main body 2 is provided with a light-shielding tab 7 adjusted to the home position index S. The passage of the light-shielding tab 7 is detected by a photo-interrupter 8 while the reel is rotated. The photo-interrupter 8 outputs a detection signal every detection of the light-shielding tab 7. The detection signal is inputted to the counter 6 as a reset pulse, thereby counted value of the counter 6 is reset to zero once a rotation.
When the step motor 5 is rotated by 1.8 degree relative to input of one drive pulse, two hundred drive pulses are required to make a rotation of the reel. And when ten symbols are arranged on the reel, twenty drive pulses are required to rotate the reel by one symbol. It is preferable to display the symbol such that the center of the symbol is substantially adjusted to a winning line when the reel is stopped. Ten drive pulses are required to rotate the reel by an interval .alpha. from the home position index S to the center of first symbol "7". If a position at which the photo-interrupter 8 is set coincides with a position of the winning line, the center of the first symbol "7" is stopped at the winning line by stopping the reel when the counted value of the counter 6 is ten.
Accordingly, in order to stop the center of the Nth symbol of the symbol sheet 3 at the winning line, the drive pulses are supplied to the step motor 5 such that the counted value of the counter 6 becomes "20N-10". In the foregoing description, the position of the winning line is adapted to coincide with the setting position of the photo-interrupter 8 for the sake of convenience. However, if the stop position of the step motor 5 is set taking a gap between the position of the winning line and the setting position of the photo-interrupter into account, it is not necessary to adjust the positions thereof.
When the symbol sheet 3 shown in FIG. 4 is used, if the symbol "7" is provided as one among ten symbols, the probability of the symbol "7" stopping at the winning line is 1/10. In case of changing the probability, the number of symbols "7" should be increased or the number of all symbols should be increased or decreased. Anyway it is required to change the symbol sheet to another one. Particularly, in case of reducing the probability of the symbol "7" to less than 1/10, the number of all symbols must be increased. According to that, stop positions of the step motor 5 must be reset. The operation of resetting the stop position is troublesome. In any case, for changing the appearance probability of the symbol, there arises a problem that changing operation is troublesome.
The appearance probability of specific symbol may be determined by software without regard to number of symbols arranged on the symbol sheet. When reel stopping control is performed such as to stop the symbol selected on the basis of the probability determined by software at the winning line, a difficult hardware change is not required. However, the appearance probability of the specific symbol determined by software would then have no relation with that of the physical reel. In other words, although the appearance probability of the symbol "7" is 1/10 relative to physical reel, it may be changed to any value, for example 1/15, by software. In such a manner, the number of stop positions determined by software does not coincide with that of the physical reel. That is not preferable.